1. Field of the Invention
The invention relates to a shift control apparatus and a shift control method for an automatic transmission of a vehicle, and particularly to improvement of a shift control apparatus and a shift control method that limit shifting of the automatic transmission based on the drive conditions of the vehicle and the driver's operations so as to appropriately control the shifting of the automatic transmission, for example, when the vehicle is running on an uphill road.
2. Description of the Related Art
A shift control apparatus for an automatic transmission, which automatically shifts the automatic transmission according to a given shift manner that is defined as, for example, a shift map using the vehicle speed and the accelerator operation amount as parameters, includes shift manner changing means for changing the shift manner based on the drive conditions of the vehicle and the driver's operations. One example of such a shift control apparatus is described in JP-A-10-238625. The shift control apparatus described in this publication, when the accelerator pedal is quickly released, holds the automatic transmission at the present speed by prohibiting upshift of the automatic transmission, so as to apply a desired drive power source brake force to the vehicle while it is cornering, or so as to eliminate the need for the automatic transmission to be shifted down to accelerate the vehicle again after cornering, that is, so as to prevent busy shifting of the automatic transmission (shifting the transmission up and down in a short period of time). As such, the shift control apparatus described in JP-A-10-238625 enables the driver to maneuver the vehicle easily when the vehicle is cornering. Another example of the shift manner changing means performs uphill and downhill drive control. Specifically, this shift manner changing means detects, based on the degree of the throttle opening, the speed of the vehicle, etc., that the vehicle is running on an uphill road or a downhill road. When the vehicle is running on an uphill road, the shift manner changing means minimizes unnecessary upshifts of the automatic transmission so that an appropriate drive power is continuously obtained. Conversely, when the vehicle is running on a downhill road, the shift manner changing means automatically shifts the automatic transmission down so that an appropriate drive power source brake force is obtained.
Typically, a shift control apparatus including such shift manner changing means has (a) an automatic shift mode in which the automatic transmission is automatically shifted using the entire shift range of the automatic transmission and (b) a manual shift mode in which the shift range of the automatic shifting performed according to the shift manner is limited according to a manual operation of the driver. In the manual shift mode, the driver manually switches the shift range of the automatic transmission among two or more shift ranges having different top speeds and the automatic transmission is automatically shifted using the speeds in each shift range selected in the manual mode. For example, when the vehicle is running on a downhill road, shifting the automatic transmission down by switching the shift range of the automatic transmission to a lower shift range increases the drive power source brake force. Meanwhile, in the automatic shift mode, the shift manner changing means changes the shift manner so as to enable the driver to maneuver the vehicle as easily as possible. Usually, in the manual shift mode, the shift manner changing means does not change the shift manner because the driver wishes to shift the automatic transmission as he or she intends in the manual shift mode.
However, in some of automatic transmissions having such a manual shift mode, even when the manual shift mode is selected, the automatic shifting is performed in the shift ranges except a specific high-speed shift range or ranges, and therefore, busy shifting sometimes occurs depending upon the drive conditions of the vehicle, as it does in the automatic shift mode. Because such busy shifting is not intended by the driver, it is desirable, to perform the control for preventing busy shifting as in the automatic shift mode. However, if the control of the shift manner changing means is used in the manual shift mode as it is, it may cause the automatic transmission to be shifted down or held at a specific speed despite the intention of the driver, which impairs the advantage of the manual shift mode. The shift manner changing means does not always perform the control for preventing busy shifting and the control of the drive power source brake force separately. That is, the shift manner changing means performs these controls cooperatively under given conditions, such as when the vehicle is running on an uphill road and when the vehicle is cornering. Therefore, it is difficult to extract the busy-shifting preventing function and use it in the manual shift mode. Meanwhile, because there are a large number of vehicle models, it takes a tremendous amount of time and cost to prepare a new control program that is exclusively used to prevent busy shifting in the manual shift mode, so it is not realistic.
It is an object of the invention to provide a shift control apparatus and a shift control method for an automatic transmission including shift manner changing means for controlling the drive power source brake and preventing busy shifting of the automatic transmission, which provides a busy-shifting preventing function for the manual shift mode in a simple form and at a low cost by utilizing the shift manner changing means.